Crank case heater control

ABSTRACT

A control system for a crank case heater for an inverter operated compressor of a cooling system includes a contactor operably connected to the crank case heater and an inverter controller compressor and at least one compressor temperature sensor disposed at the compressor to sense a compressor temperature and an compressor internal temperature sensor. A controller is operably connected to the crank case heater and the at least one compressor temperature sensor and configured to close the contactor to energize the crank case heater independently from operation of the compressor when the at least one compressor temperature sensor senses a compressor temperature below a desired threshold.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to cooling systems. Morespecifically, the subject disclosure relates to control of a crank caseheater for a variable speed compressor of such systems.

A crank case heater is an electrical component option used on coolingsystems such as air conditioners, heat pumps or chillers. In a coolingsystem, refrigerant always tends to migrate towards a lowest temperatureportion of the system when the refrigeration system is not operating,specifically when the compressor not operating. The compressor isgenerally the largest thermal mass in the refrigeration system. Due tonormal day to night temperature swings, the temperature around thecompressor changes in split system and packaged air conditioners andheat pumps. As the temperature warms from a cold or chilly night, thecompressor is often the coldest point in the system due the time ittakes for the compressor to change temperatures compared to othercomponents. Due to the inherent design of hermetic and semi-hermeticcompressors, when the compressor is the coldest point in the system andwhen the cooling system is shut off, the refrigerant vapor will thencondense in the compressor and mix with the compressor crank case oil.On the next start of the compressor the oil/refrigerant mixture tends towash out the lubricant from the bearings in the compressor, leading towear to the point that sometimes causes bearings in the compressor tolocked up, or gall to a point resulting in an unusable compressor. Tomitigate this problem, crank case heaters are often utilized to preventthe compressor from being the lowest temperature component of thesystem, thereby preventing migration of refrigerant to the compressorcrankcase.

The crankcase heater is a resistance heater installed either in(insertion type) or around (belly band type) a compressor of a coolingsystem. When a voltage is applied across the crank case heater, itproduces heat which migrates to the compressor to heat the compressorcrank case. A typical crank case heater wired across the contactor whichoperates the compressor. When the contactor is in an open position aswhen the compressor is not operating, the crank case heater is in serieswith the compressor windings. Current flows through the compressorwindings and powers the crank case heater. When the contactor is closed,the compressor is operating and the crank case heater is off becausethere is no potential across the crank case heater. Thus, in the typicalsystem, whenever the compressor is off, the crank case heater isoperating, whether necessary or not.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a control system for a crankcase heater for an inverter-operated variable speed compressor of acooling system includes a contactor operably connected to the crank caseheater and the inverter and at least one compressor temperature sensorlocated at the compressor to sense a compressor temperature. Atemperature switch is located at a discharge line of the compressor, anda controller is operably connected to the crank case heater and the atleast one compressor internal temperature sensor. The control isconfigured to close the contactor to energize the crank case heater whenthe at least one compressor temperature sensor senses a compressortemperature below a desired threshold.

According to another aspect of the invention, a cooling system includesan inverter operably connected to a compressor,

According to another aspect of the invention, a cooling system includesan inverter, a compressor, a crank case heater disposed at thecompressor, and a contactor operably connected to the inverter and thecrank case heater. At least one compressor temperature sensor is locatedat the compressor to sense a compressor temperature. A controller isoperably connected to the crank case heater and the at least onecompressor temperature sensor and configured to close the contactor toenergize the crank case heater independently from operation of thecompressor when the at least one compressor temperature sensor senses acompressor temperature below a desired threshold.

According to yet another aspect of the invention, a method ofcontrolling operation of a crank case heater for a compressor of acooling system includes sensing a compressor temperature and determiningif the compressor temperature is below a desired threshold. A contactoroperably connected to the inverter and the crank case heater is closed,thereby energizing the crank case heater if the compressor temperatureis below the desired threshold, wherein energizing of the crank caseheater is independent of operation of the compressor.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

The FIGURE is a schematic of a crank case heater and compressorarrangement.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Shown in the FIGURE is schematic of an embodiment of a crank case heater(CCH) 10, an inverter 16 and compressor 12 as arranged in a coolingsystem. In this arrangement, the compressor 12 is connected to acontactor 14 indirectly via an inverter 16. A controller is alsoconnected to an outdoor ambient temperature sensor and an indoortemperature sensor. The inverter 16 is powered by the contactor 14 and acontroller 18 is utilized to determine when to send a signal to theinverter 16 directing the inverter to power the compressor 12. Thus, thecontactor 14 can be closed by a signal from a controller withoutnecessarily supplying power to the compressor 12.

The CCH 10 is wired in series with the contactor 14 and with a dischargeline temperature switch, or thermostat 20, that assesses a temperatureof the compressor discharge line and is located at a discharge line 22of the compressor 12. When it is desired to energize the CCH 10, thecontroller 18 sends a signal to the contactor 14 to close the contactor14 thus applying a voltage across the CCH 10. The decision to energizethe CCH 10 is based on a compressor temperature sensed by a compressortemperature sensor 24 located, for example, internal to the compressor12, and the indoor temperature and the outdoor temperature. If thecompressor temperature sensor 24 senses a compressor temperature above adesired upper limit, the contactor 14 will be opened causing the CCH 10to not be powered. If, on the other hand, the compressor temperaturesensor 24 senses a compressor temperature below a desired lower limitwhile the compressor 12 is not running, the thermostat 20 switch will beclosed (because the compressor 12 is not running) and the CCH 10 will bepowered given that the contactor 14 is closed. For example, in someembodiments, the CCH 10 will be powered if the compressor temperaturesensor 24 determines that the compressor temperature is below an indoortemperature of a dwelling 26 at which the system is installed and isless than 25 degrees Fahrenheit above an outdoor ambient temperature asdetermined by dwelling temperature sensors 28 and outdoor ambienttemperature sensors 30 connected to the controller 18, and thethermostat 20 senses a discharge line 22 temperature below a dischargeline threshold temperature.

The threshold limits are established based on physics consisting ofindoor and outdoor temperature, the power of the crank case heater 10and the thermal time constant of the compressor 12. A delta is added tothe compressor temperature to ensure changing outdoor ambient do notcause the compressor 12 to become colder than the outdoor ambient. Thisensures the compressor 12 is never the coldest refrigerant component inthe system.

This arrangement and control method utilizes sensed temperatures tocontrol operation of the CCH 10 rather than always operating the CCH 10when the compressor 12 is off, and not operating the CCH 10 when thecompressor 12 is on, as in the prior art. This allows for limiting theoperation if the CCH 10 when the compressor is operating and alsolimiting the CCH 10 operation at higher outdoor ambient temperatures,when operation of the CCH may not be necessary, thus saving energy andpreserving operational life of the CCH 10.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A control system for a crank case heater for a compressor of acooling system comprising: a contactor operably connected to the crankcase heater, the inverter and indirectly to the compressor; at least onecompressor temperature sensor disposed at the compressor to sense acompressor temperature; a first temperature switch located in air space;and a controller operably connected to the crank case heater and the atleast one compressor temperature sensor and configured to close thecontactor to energize the crank case heater when the at least onecompressor temperature sensor senses a compressor temperature below adesired threshold; and a second temperature switch located at adischarge line of the compressor to energize the crank case heater whena discharge line temperature is below a desired lower limit and thecompressor is not operating.
 2. The control system of claim 1, whereinthe controller is operably connected to the compressor.
 3. The controlsystem of claim 2, wherein the controller is configured to energize thecompressor independently of the crank case heater via the secondtemperature switch.
 4. The control system of claim 2, wherein thecontroller is operably connected to the compressor via the inverter. 5.The control system of claim 1, wherein at least one compressortemperature sensor is disposed internal to the compressor.
 6. Thecontrol system of claim 1, wherein the first temperature switch is in anindoor ambient air space.
 7. The control system of claim 1 wherein thefirst temperature switch is in an outdoor ambient air space.
 8. Thecontrol system of claim 1, wherein the threshold is determined relativeto the lesser of a dwelling temperature and an outdoor ambienttemperature plus a differential value.
 9. The control system of claim 8,further comprising at least one dwelling temperature sensor operablyconnected to the controller.
 10. The control system of claim 8, furthercomprising at least one ambient temperature sensor operably connected tothe controller.
 11. A cooling system comprising: a compressor; aninverter a crank case heater disposed at the compressor; a contactoroperably connected to the inverter and the crank case heater; at leastone compressor temperature sensor disposed at the compressor to sense acompressor temperature; and a controller operably connected to the crankcase heater and the at least one compressor temperature sensor andconfigured to close the contactor to energize the crank case heater whenthe at least one compressor temperature sensor senses a compressortemperature below a desired threshold; and a temperature switch locatedat a discharge line of the compressor to energize the crank case heaterwhen a discharge line temperature is below a desired lower limit and thecompressor is not operating.
 12. The cooling system of claim 11, whereinthe controller is operably connected to the inverter.
 13. The coolingsystem of claim 12, wherein the controller is configured to energize thecompressor independent of operation of the crank case heater.
 14. Thecooling system of claim 12, wherein the controller is operably connectedto the compressor via an inverter.
 15. The cooling system of claim 14,wherein the inverter is connected to the contactor.
 16. The coolingsystem of claim 11, wherein the at least one compressor temperaturesensor is disposed internal to the compressor.
 17. The cooling system ofclaim 11, further comprising at least one dwelling temperature sensoroperably connected to the controller.
 18. The cooling system of claim11, further comprising at least one outdoor ambient temperature sensoroperably connected to the controller.
 19. A method of controllingoperation of a crank case heater for a compressor of a cooling systemcomprising: sensing a compressor temperature; determining if thecompressor temperature is below a desired threshold; closing a contactoroperably connected to the compressor and the crank case heater, therebyenergizing the crank case heater if the compressor temperature is belowthe desired threshold; wherein energizing of the crank case heater isindependent of operation of the compressor.
 20. The method of claim 19,further comprising deengerizing the crank case heater when thecompressor temperature is above the desired threshold.
 21. The method ofclaim 19, further comprising deengerizing the crank case heater when thecompressor discharge line temperature is above the desired threshold.22. The method of claim 19, wherein the threshold is determined relativeto the lesser of a dwelling temperature and an outdoor ambienttemperature.